I liked how the Template Numerical Toolkit implemented one-based indexing:

    // Construct matrix. Elements are not initialized.
    // To initialize all elements to zero use
    // Matrix<double> a(2, 2, 0.0).
    Matrix<double> a(2, 2);
    
    // Assign elements to first row using
    // Fortran-style one-based indexing.
    a(1,1) = 0.5; a(1,2) = 1.0;
    
    // Assign elements to second row using
    // C-style zero-based indexing.
    a[1][0] = 1.5; a[1][1] = 2.0;

-- http://www.b-a-h.com/software/cpp/scppnt.html